Semiconductor local interconnect and contact

ABSTRACT

An integrated circuit is provided. A gate dielectric and a gate are provided respectively on and over a semiconductor substrate. A junction is formed adjacent the gate dielectric and a shaped spacer is formed around the gate. A spacer is formed under the shaped spacer and a liner is formed under the spacer. A first dielectric layer is formed over the semiconductor substrate, the shaped spacer, the spacer, the liner, and the gate. A second dielectric layer is formed over the first dielectric layer. A local interconnect opening is formed in the second dielectric layer down to the first dielectric layer. The local interconnect opening in the first dielectric layer is opened to expose the junction in the semiconductor substrate and the first gate. The local interconnect openings in the first and second dielectric layers are filled with a conductive material.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This is a divisional of application Ser. No. 10/359,975 filed Feb. 7,2003, which is hereby incorporated by reference herein now U.S. Pat. No.6,884,712.

BACKGROUND

1. Technical Field

The present invention relates generally to integrated circuits, and morespecifically to local interconnects and isolated contacts forinterconnecting semiconductor devices.

2. Background Art

As semiconductor technology continues to evolve, a continuing trend istowards ultra large-scale integration with the fabrication of smallerand smaller integrated circuits with more and faster semiconductordevices.

Fabrication of an integrated circuit involves numerous processing steps.After doped regions have been deposited to form source/drain junctionswithin a semiconductor substrate and gates have been defined on thesubstrate, dielectric layers are deposited on the semiconductor devicesand conductors are routed over the dielectric layers to connect to andfill openings formed through the dielectric layer to the source/drainjunctions and gates. The entire process of routing and makingconnections is generally termed “metalization”. The term derives itsorigins from interconnect technology, where metals were the firstconductors used, but encompasses both metals and conductive materialssuch as polysilicon. As the complexity of integrated circuit isincreased, the complexity of metalization has also increased.

At the same time that the complexity of metallization has increased,multiple layers of interconnect structures have been have come into useas well as short distance interconnects at levels at or below thecustomary metallization layers. The latter are termed “localinterconnects” and are a special form of interconnects for very shortdistances, such as between the gate and drain of an individualsemiconductor device.

A commonly used technique for forming local interconnects is thedamascene process. This process involves depositing a dielectric layerover the semiconductor device and then polishing the dielectric layer tomake the layer planar. The layer is then patterned and etched to formopenings down to the underlying gate or source/drain junctions. Aconductor is then deposited in the openings and a chemical-mechanicalpolishing process (CMP) is used to damascene a conductor into dielectriclayer to form the local interconnects and isolated contacts.

There are a number of problems with existing processes such as thosecaused by larger openings etching at a different rate than smalleropenings. This means that the larger local interconnect contacts whichhave larger openings than the isolated contacts will be completed beforethe isolated contact openings are open to the source/drain junctions.This is especially true for very small isolated contact openings betweenvery tightly spaced gates (especially at 0.18μ or lower).

Further, the process window for time for etching openings becomes veryshort when trying to create the different sized isolated contacts andlocal interconnects. This is especially true at 0.16μ or lower, wherethe local interconnects are three to four times larger than the isolatedcontacts. In these cases, the processes often result in gouging of theshallow trench isolations, which separate the semiconductor devices, andloss of isolating spacers.

Also, incomplete filling results in a void area, also known as a“keyhole,” that is formed within the metalization. This keyhole isdetrimental because it can open up during further processing steps,where material which could corrode or corrupt the tungsten layer canmake its way into the keyhole. Also, the void in the center of theconducting metalization layer in the contact causes an increase incontact resistance.

Solutions to problems of this sort have been long sought, but there hasbeen no teaching or suggestion in the prior art how those havingordinary skill in the art could solve these problems.

DISCLOSURE OF THE INVENTION

The present invention provides for an integrated circuit with asemiconductor substrate having a first gate dielectric and a first gateprovided thereon and thereover. A lightly doped drain is formed in thesemiconductor substrate adjacent the gate dielectric, and a spacer lineris formed on the substrate around the first gate dielectric and thefirst gate. A first spacer is formed on the spacer liner and around thefirst gate. A second spacer is formed on the first spacer and around thefirst gate. A first dielectric layer is formed over the semiconductorsubstrate, the spacer liner, the first and second spacers, and the firstgate. A second dielectric layer is formed over the first dielectriclayer. A local interconnect opening is formed in the second dielectriclayer down to the first dielectric layer. The local interconnect openingin the first dielectric layer is opened to expose the junction in thesemiconductor substrate and the first gate. The local interconnectopenings in the first and second dielectric layers are filled with aconductive material.

Certain embodiments of the invention have other advantages in additionto or in place of those mentioned above. The advantages will becomeapparent to those skilled in the art from a reading of the followingdetailed description when taken with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of an integrated circuit in an intermediate stage ofmanufacture in accordance with the present invention;

FIG. 2 is the structure of FIG. 1 after further processing;

FIG. 3 is the structure of FIG. 2 after further etching;

FIG. 4 is the structure of FIG. 3 after deposition and processing of twointerlayer dielectric layers;

FIG. 5 is the structure of FIG. 4 after further processing; and

FIG. 6 is a simplified flow chart of the method of manufacturing anintegrated circuit in accordance with the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to FIG. 1, therein is shown an integrated circuit 100 inan intermediate stage of manufacture. The integrated circuit 100includes a semiconductor substrate 102 having first and second gatedielectrics 104 and 106 formed on the surface of the semiconductorsubstrate 102 under first and second semiconductor gates 108 and 110,respectively.

The term “horizontal” as used in herein is defined as a plane parallelto the conventional plane or surface of a wafer or substrate, regardlessof its orientation. The term “vertical” refers to a directionperpendicular to the horizontal as just defined. Terms, such as “on”,“above”, “below”, “side” (as in “sidewall”), “higher”, “lower”, “over”,and “under”, are defined with respect to the horizontal plane. The term“processing” as used herein includes deposition of material orphotoresist, patterning, exposure, development, etching, cleaning,and/or removal of the material or photoresist as required in forming adescribed structure.

The first and second semiconductor gates 108 and 110 have been used toimplant lightly doped source/drain junctions 112 in the semiconductorsubstrate 102. The lightly doped source/drain junctions 112 of differentsemiconductor devices, such as the first and second semiconductordevices 114 and 116, are separated by shallow trench isolations, such asa shallow trench isolation 120.

A spacer liner layer 121 is deposited over the semiconductor substrate102, the first and second semiconductor gates 108 and 110, and theshallow trench isolation 120. A first spacer layer 122 is deposited overthe spacer liner layer 121.

Referring now to FIG. 2, therein is shown the structure of FIG. 1 afterfurther processing. A second spacer layer 124, shown by dotted lines,has been deposited, and then isotropically etched to form first andsecond shaped spacers 126 and 128 respectively around the first andsecond semiconductor gates 108 and 110.

Referring now to FIG. 3, therein is shown the structure of FIG. 2 afterfurther etching. Isotropic etches have been used to expose thesemiconductor substrate 102, the shallow trench isolation 120, and thetops of the first and second semiconductor gates 108 and 110. Theseetching steps forms the spacer liner layer 121 of FIG. 2 into first andsecond L-shaped liners 132 and 134 and the first spacer layer 122 ofFIG. 2 into first and second L-shaped spacers 136 and 138 respectivelyaround the first and second semiconductor gates 108 and 110. Theselectivity of the etch will be such that the first and second L-shapedspacers 136 and 138 will substantially protect the first and secondL-shaped liners 132 and 134 during the etching of the spacer liner layer121 of FIG. 2.

The first and second shaped spacers 126 and 128, the first and secondL-shaped liners 132 and 134, and the first and second L-shaped spacers136 and 138 are used along with the first and second semiconductor gates108 and 110 during the implantation of deep source/drain junctions 130.The deep source/drain junctions 130 may also be salicided to providebetter electrical contact.

Referring now to FIG. 4, therein is shown the structure of FIG. 3 afterdeposition and processing of two interlayer dielectric layers. A firstinterlayer dielectric layer 140 is deposited over the semiconductorsubstrate 102, the shallow trench isolation 120, the first and secondshaped spacers 126 and 128, the first and second L-shaped liners 132 and134, the first and second L-shaped spacers 136 and 138, and the firstand second semiconductor gates 108 and 110.

A second interlayer dielectric layer 142 is deposited over the firstinterlayer dielectric layer 140. An anisotropic etching process has beenperformed into the second interlayer dielectric layer 142 to form alocal interconnect opening 144 and a isolated contact opening 146. Thetwo openings are of different sizes but the etch selectivity is suchthat both openings end at the first interlayer dielectric layer 140;i.e., etching essentially stops at the first interlayer dielectric layer140 even though the etch may be applied for a substantially long lengthof time. This compensates for the different etch rates due to thedifferent sizes of the local interconnect opening 144 and the isolatedcontact opening 146, and provides a very long process window.

Referring now to FIG. 5, therein is shown the structure of FIG. 4 afterfurther processing. An etching process has been applied to the localinterconnect opening 144 of FIG. 4 and the isolated contact opening 146of FIG. 4 to remove the first interlayer dielectric layer 140 in theopenings. The etching step exposes the top of the first semiconductorgate 108, the semiconductor substrate 102 over the deep source/drainjunctions 130 on both sides of the shallow trench isolation 120, and theshallow trench isolation 120.

It will be noted that the first and second L-shaped liners 132 and 134are slightly etched away under the first and second L-shaped spacers 136and 138, respectively, but are substantially protected thereby. Thefirst L-shaped spacer 136 is exposed to the etching in the localinterconnect opening 144 of FIG. 4, and is slightly etched away butremains substantially intact.

The present invention has a number of advantages. The first shapedspacer 126 prevents punch-through of the first L-shaped spacer 136 andthe first L-shaped liner 132. There is also no, or lower, probability ofjunction spiking during local interconnect formation. This is becomingmore important as the technology advances because all the junctionsbecome shallower and shallower, and it is necessary not to etch into thesubstrate, which contains the lightly doped source/drains junctions.

It will also be understood that in certain devices, the local areainterconnect is required; for example, to reduce the SRAM per bit area.In these devices, the protection of the first shaped spacer 126 isrequired for lower current consumption by reducing junction leakage.

After the etching, the local interconnect opening 144 of FIG. 4 and theisolated contact opening 146 of FIG. 4 are filled with conductormaterial to form a local interconnect 150 and an isolated contact 152.

Based on the disclosure above it would be evident to those havingordinary skill in the art that different materials may be used providedthat they have the proper selectivity to the etch being used in thevarious steps. For example, in one embodiment, the spacer liner layer121 of FIG. 1 can be a silicon oxide and the first spacer layer 122 ofFIG. 1 can be silicon nitride. If a salicide stop layer is required, thesalicide stop layer can be silicon oxide and the spacer liner layer 121will be silicon nitride. The other materials would be adjustedaccordingly.

The first and second shaped spacers 126 and 128 of FIG. 2 can be ofsilicon oxide and the first interlayer dielectric layer 140 of FIG. 4can be silicon nitride or silicon oxynitride. The second interlayerdielectric layer 142 can be of silicon oxide, or a low-dielectricconstant dielectric material.

The conductive material for the local interconnect 150 and the isolatedcontact 152 can be of a conductive material such as tungsten (W),tantalum (Ta), titanium (Ti), alloys thereof, and compounds thereof orconductive materials such as copper (Cu), aluminum (Al), alloys thereof,and compounds thereof with appropriate barrier layers.

Referring now to FIGS. 6A and 6B, therein is shown a simplified flowchart of a method 200 in accordance with the present invention. Themethod 200 includes:

-   -   a step 202 of providing a semiconductor substrate having a first        gate dielectric and a first gate respectively on and over the        semiconductor substrate;    -   a step 204 of forming a junction in the semiconductor substrate        adjacent the gate dielectric;    -   a step 206 of forming a first shaped spacer around the first        gate;    -   a step 208 of forming a first spacer under the first shaped        spacer;    -   a step 210 of forming a first liner under the first spacer over        the semiconductor substrate;    -   a step 212 of forming a first dielectric layer over the        semiconductor substrate and the first gate;    -   a step 214 of forming a second dielectric layer over the first        dielectric layer;    -   a step 216 of forming a local interconnect opening in the second        dielectric layer to the first dielectric layer;    -   a step 218 of opening a local interconnect opening in the first        dielectric layer exposing the first gate and the junction in the        semiconductor substrate; and    -   a step 220 of depositing a conductive material in the local        interconnect openings.

While the invention has been described in conjunction with a specificbest mode, it is to be understood that many alternatives, modifications,and variations will be apparent to those skilled in the art in light ofthe aforegoing description. Accordingly, it is intended to embrace allsuch alternatives, modifications, and variations which fall within thespirit and scope of the included claims. All matters hithertofore setforth herein or shown in the accompanying drawings are to be interpretedin an illustrative and non-limiting sense.

1. An integrated circuit comprising: a semiconductor substrate having afirst gate dielectric and a first gate respectively on and over thesemiconductor substrate, the semiconductor substrate having asource/drain junction adjacent the gate dielectric; a first L-shapedliner over the semiconductor substrate around the first gate; a firstL-shaped spacer on the first L-shaped liner; a first shaped spacer onthe first L-shaped spacer; a first dielectric layer over thesemiconductor substrate, the first L-shaped liner, the first L-shapedspacer, the first shaped spacer, and the first gate, the firstdielectric layer having a local interconnect opening provided thereinexposing the first gate and the source/drain junction in thesemiconductor substrate; a second dielectric layer over the firstdielectric layer, the second dielectric layer having a localinterconnect opening provided therein; and a conductive material in thelocal interconnect opening in the second dielectric layer and the localinterconnect opening in the first dielectric layer.
 2. The integratedcircuit as claimed in claim 1 wherein depositing the liner layer anddepositing the spacer layer deposits different materials having highetch selectivity between the different materials.
 3. The integratedcircuit as claimed in claim 1 wherein depositing the spacer layer anddepositing the shaped spacer layer deposits different materials havinghigh etch selectivity between the different materials.
 4. The integratedcircuit as claimed in claim 1 wherein the first dielectric layer and thesecond dielectric layer are of different materials having high etchselectivity between the different materials.
 5. The integrated circuitas claimed in claim 1 wherein: the semiconductor substrate has a secondgate dielectric and a second gate respectively on and over thesemiconductor substrate, the semiconductor substrate having asource/drain junction adjacent the second gate dielectric; a secondL-shaped liner is on the semiconductor substrate around the second gate;a second L-shaped spacer is on the second L-shaped liner; a secondshaped spacer is on the second L-shaped spacer; the first dielectriclayer having isolated contact opening provided therein exposing thesource/drain junction in the semiconductor substrate adjacent the secondgate dielectric; the second dielectric layer having an isolated contactopening provided therein; and the conductive material in the isolatedcontact opening in the second dielectric layer and the isolated contactopening in the first dielectric layer.